DE69602630T2 - Copolyesters, molded articles containing these polymers and aromatic triols for their manufacture - Google Patents

Abstract

A copolyester consisting essentially of ethylene terephthalate units and further comprising 0.01 to 1 mole % based on the sum of the moles of total diol units and the moles of triol units of a triol unit represented by the following formula (I) and/or a triol unit represented by the following formula (II). <CHEM> <CHEM> wherein A is a group represented by formula -CH2CH2- or formula -CH(CH3)CH2-, B is a divalent hydrocarbon group, -CO-, -SO2-, -O- or a direct bond (-), and p, q, r, s, t and u are each an integer of 1 to 8. A process for producing the same and molded articles (in particular extrusion blow molded articles) therefrom. The copolyesters of the present invention are applicable to melt moldings accompanying melt extrusion, in particular extrusion blow molding, where parisons therefrom have good draw-down tendency and blow moldability. The copolyesters can give, without causing troubles on molding, molded articles, in particular extrusion blow molded articles, having excellent transparency, heat resistance, moisture resistance and like properties. Aromatic triols usable for producing the above copolyesters are also provided.

Description

The present invention relates to copolyesters, production processes therefor and aromatic triols used in the production thereof; and further to a process for producing molded articles therefrom and molded articles obtained from the process. The copolyesters of the invention have a high melt viscosity and have the non-Newtonian properties of exhibiting low viscosity at high shear rates and high viscosity at low shear rates and are thus applicable in various molding processes, in particular extrusion blow molding, whereby hollow molded articles are produced.

Resins of polyesters, including polyethylene terephthalate, are excellent in various characteristics such as transparency, mechanical properties, gas barrier properties and taste barrier properties, and in hygiene and safety because they cause little concern about residual monomers and toxic additives when molded into articles. The resins have therefore been widely used in recent years for hollow containers to be filled with juices, soft drinks, seasonings, oil, cosmetics, cleaners and the like, replacing polyvinyl chloride resins.

Two representative processes for producing hollow molded articles, such as plastic containers, are extrusion blow molding, which involves extruding a melt-softened resin through a mold opening into a cylindrical parison and blowing a fluid, such as air, into the parison while it is still kept softened; and injection blow molding, which involves injecting a molten resin into a mold, thereby once forming a closed parison (preforms), and, after being placed in a blow mold, blowing a fluid, such as air, into the preforms.

Of the above methods, the former, i.e. extrusion blow molding, is simpler than the latter, i.e. injection blow molding, and does not require high techniques in mold making and molding and thus requires only the cost of equipment and mold making. Extrusion blow molding is therefore suitable for manufacturing multiple products in small quantities and has the further advantage that it can manufacture thin, thick or large articles and complex-shaped parts with a button or similar irregular components.

Therefore, various attempts have been made to carry out extrusion blow molding with general-purpose polyesters such as polyethylene terephthalate and polybutylene terephthalate. However, general-purpose polyesters generally have a low melt viscosity, so that when they are extrusion blow molded, the extruded parisons sag (sink) noticeably and become difficult to mold. In addition, crystallization may occur during blow molding after extrusion, thereby deteriorating transparency or moldability. These disadvantages of conventional polyesters, which are caused by their low melt viscosity and easy crystallizability, are more pronounced when they are extrusion blow molded into long parisons having a length of generally 20 cm or more, which is required for the production of large hollow molded articles. As a result, it becomes very difficult to obtain molded articles, especially large ones, having a uniform shape and size and at the same time good transparency from conventional polyesters by extrusion blow molding.

For the above reason, in carrying out extrusion blow molding, polyvinyl chloride and polyolefin resins have been used which have a high melt viscosity and which cause little sagging of the extruded parisons in the molten state. However, extrusion blow molded articles made of polyvinyl chloride resin have some problems in terms of hygiene or safety in terms of leaching of toxic additives such as plasticizers and metal-containing stabilizers and in that incineration of waste from the molded articles generates toxic gases. Their use has therefore decreased in Europe and other areas. Extrusion blow molding with polyolefins such as polyethylene causes the resulting molded articles to become cloudy white due to crystals, so that the articles tend to have poor transparency and poor appearance.

In view of the above, several proposals have been made regarding polyester resins applicable to extrusion blow molding, including:

1. US-A-4,161,579, 4,219,527, 4,234,708 and 4,182,841 and JP-A-55-92 730 (1980) disclose a process for producing polyester applicable to extrusion blow molding which comprises esterifying or transesterifying a dicarboxylic acid component such as terephthalic acid or ester-forming derivatives thereof with a diol component such as ethylene glycol to obtain a compound having a low degree of polymerization, reacting a conventional crosslinking agent such as trimethylolpropane, pentaerythritol or trimellitic acid with the compound to produce a prepolymer, and polymerizing the prepolymer in solid phase;

2. in the production of polyethylene terephthalate, polybutylene terephthalate or the like, a method comprising copolymerizing isophthalic acid or cyclohexanedimethanol is known; and

3. EP-A-0 532 943 discloses a process for producing modified polyesters which comprises adding an ethylene oxide adduct of bisphenol A in the production of polyethylene terephthalate, polybutylene terephthalate or the like.

However, polyesters obtained by the above method 1 give extrusion blow molded articles without transparency with pronounced whitening due to the generation of spherulites resulting from the increased crystallization rate. Furthermore, in some cases, gels are formed due to crosslinking and cause the resulting molded articles to contain agglomerates, thereby deteriorating their appearance.

The present inventors, based on the above prior art 2, prepared polyethylene terephthalate-based copolymers having a reduced melting point by copolymerizing isophthalic acid or cyclohexanedimethanol, and attempted to carry out extrusion blow molding of these copolyesters with the melt extrusion temperature set at a lower temperature than before. However, since the melt viscosity at the extrusion temperature was not sufficiently high, the extruded parisons sagged noticeably during extrusion and were difficult to mold, so that the extrusion blow molding could not be carried out smoothly. Furthermore, with the copolyesters copolymerized with isophthalic acid or cyclohexanedimethanol obtained by the prior art 2, solid-phase polymerization could not be carried out, or if it was ever carried out, it proceeded too slowly to achieve a sufficiently high degree of polymerization. As a result, molded parts made from these copolyesters had a large variation in thickness and poor transparency.

The present inventors also conducted a follow-up experiment on the copolyester of the above 3 according to the known technique, which was copolymerized with an ethylene oxide adduct of bisphenol A, and found that its extrusion blowability was not sufficiently good.

The present inventors also attempted to produce a polyethylene terephthalate having a high degree of polymerization by means of solid phase polymerization, other than the known techniques of the above 1 to 3. However, it was found that the rate of solid phase polymerization was very low, so that it was impossible to produce in a short period of time and efficiently a polyethylene terephthalate having a sufficiently high degree of polymerization and a polymerization suitable for extrusion blow molding and the like. melt viscosity. This method is therefore not applicable in practice from the point of view of productivity.

EP-A-0 119 731 relates to polyethylene terephthalate copolyesters having an increased crystallization time due to a diol unit carrying a sulfone group.

Accordingly, it is an object of the present invention to provide a polyester having excellent melt moldability and high melt viscosity, particularly excellent extrusion blowability, which, when extrusion blown, can give an extruded parison causing no severe sagging and molded articles having a desired shape and size with high precision and smoothly.

Another object of the present invention is to provide a polyester which can smoothly give molded articles having excellent transparency and heat resistance in melt molding, particularly in extrusion blow molding.

Another object of the present invention is to provide a process for producing in a short period of time and with high productivity polyesters having the above excellent features.

Still another object of the present invention is to provide a process for producing molded articles from the above polyesters having excellent characteristics by melt molding, particularly extrusion blow molding, and also to provide molded articles obtained thereby.

Still another object of the present invention is to provide an aromatic triol which does not produce gel-like agglomerates and has a great effect on increasing the polymerization rate and is therefore useful as a crosslinking agent and a resin modifier.

The above objects have been achieved by the surprising finding that in the production of polyester from a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof and a diol component consisting essentially of ethylene glycol, 1 the use of a certain amount of a certain triol component having a benzene ring results in the production of a copolyester which is excellent in the above melt-formability and at the same time in transparency and heat resistance, and 2 the use of a certain amount of the above certain triol in combination with a certain amount of a certain diol having a benzene ring can give a copolyester having excellent mechanical properties such as impact resistance as well as having the above excellent melt-formability, transparency and heat resistance. It was also found that the copolyesters can be obtained in a short period of time and with good productivity by esterifying or transesterifying the above dicarboxylic acid component, diol components and triol component, melt-condensing the obtained reaction product to produce a prepolymer, and polymerizing the prepolymer in solid phase.

A further study was made on the properties and moldability of the above high melt viscosity copolyesters developed by them, and the following facts were found. That is, the copolyesters exhibit non-Newtonian properties, having a low viscosity at high shear rates and a high viscosity at low shear rates, and thus are suitable for various melt molding processes, particularly extrusion blow molding. When extrusion blow molded, the copolyesters give parisons which do not cause severe sagging and thus have good blow moldability. With the copolyesters, it is possible to smoothly produce molded parts having the desired shape and size with high accuracy and high productivity, and the parts are excellent in transparency, mechanical properties, heat resistance and the like. Based on these findings, the present inventors have completed the invention.

The present invention provides a copolyester (hereinafter sometimes referred to as "copolyester (A)") comprising:

(i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, wherein the copolyester further comprises:

(ii) at least one group of triol units selected from:

(a) Triol units (I) of the following formula (I)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8; and

(b) Triol units (II) of the following formula (II)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂ and s, t and u are each independently an integer from 1 to 8, in an amount of 0.01 to 1 mol% based on the sum of the number of moles of the total diol units and the number of moles of the triol units of this item (ii).

The present invention also provides a copolyester (hereinafter sometimes referred to as "copolyester (B)") comprising:

(i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, wherein the copolyester further comprises:

(ii) at least one group of diol units selected from:

(a) Diol units (III) of the following formula (III)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and j and k are each independently an integer from 1 to 8; and

(b) Diol units (IV) of the following formula (IV)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and m and n are each independently an integer from 1 to 8, and

(iii) at least one group of triol units selected from:

(a) Triol units (I) of the following formula (I)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8; and

(b) Triol units (II) of the following formula (II)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and s, t and u are each independently an integer from 1 to 8, and

(iv) wherein the at least one group of diol units selected from diol units (III) and diol units (IV) is contained in an amount of 1 to 15 mol% based on the sum of the number of moles of the total diol units and the number of moles of the triol units of the above point (iii), and

(v) wherein the at least one group of triol units selected from triol units (I) and triol units (II) is contained in an amount of 0.01 to 1 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the triol units of the above item (iii).

The present invention further relates to molded parts, in particular extrusion molded parts, and also to a process for producing molded parts from the above copolyesters by means of extrusion blow molding.

The present invention further provides a process for producing the above copolyester (A), which comprises:

Esterification or transesterification of starting materials, comprising:

(1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof;

(2) a diol component consisting essentially of ethylene glycol; and

(3) a triol component comprising at least one triol selected from:

(a) a triol of the following formula (V):

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8; and

(b) a triol of the following formula (VI)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and s, t and u are each independently an integer from 1 to 8 ;

in an amount of 0.01 to 1 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol component of this item (3);

melt polycondensing the resulting reaction product to produce a polyester prepolymer; and

Polymerizing the polyester prepolymer in solid phase.

The present invention further provides a process for producing the above copolyester (B), which comprises:

Esterification or transesterification of starting materials, comprising:

(1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof;

(2) a diol component consisting essentially of ethylene glycol and at least one diol selected from

(a) a diol of the following formula (VII)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and j and k are each independently an integer from 1 to 8; and (b) a diol of the following formula (VIII)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and m and n are each independently an integer from 1 to 8 ;

in an amount of 1 to 15 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the triol component of the item (3) described below; and

(3) a triol component containing at least one triol selected from a triol of the above formula (V) and a triol of the above formula (VI) in an amount of 0.01 to 1 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the triol component of this item (3);

melt polycondensing the resulting reaction product to produce a polyester prepolymer; and

Polymerizing the polyester prepolymer in solid phase.

The present invention further provides an aromatic triol of the following formula (V)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8;

and an aromatic triol component of the following formula (VI)

in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and

s, t and u are each independently an integer from 1 to 8.

The copolyesters (A) and (B) of the present invention (hereinafter collectively referred to as "copolyesters") mainly comprise diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, and it is necessary that these copolyesters further comprise, together with the above diol units and dicarboxylic acid units, at least one group of units selected from triol units (I) of the above formula (I) and triol units (II) of the above formula (II).

The copolyesters according to the invention can comprise either one or both of the triol units (I) and triol units (II) as triol units.

In the triol units (I) and triol units (II), the radical A is a radical (ethylene group) of the formula -CH₂CH₂- or a radical (1,2-propylene group) of the formula -CH(CH₃)CH₂-. In the copolyesters according to the invention and the triol units (I) and/or Triol units (II), all the A residues may be an ethylene group, all the A residues may be a 1,2-propylene group, or part of the residues may be an ethylene group while the remainder is a 1,2-propylene group. Of these cases, in view of the ease of preparation of the copolyesters and the production cost, it is desirable that in the copolyesters the A residue in the triol units (I) and/or triol units (II) is the ethylene group.

The residue B in the triol units (I) is a divalent hydrocarbon residue, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-). When the B radical is a divalent hydrocarbon radical, the radical is desirably an alkylene radical or alkylidene radical having 1 to 8 carbon atoms or a divalent aromatic radical. Specific examples of desirable divalent hydrocarbon radicals are the methylene, ethylene, ethylidene, 1,2-propylene, propylidene, trimethylene, isopropylidene, butylidene, ethylethylene, tetramethylene, 1-methylpropylidene,1,2-dimethylethylene, pentylidene, 1-methylbutylidene, pentamethylene,1-ethyl-2-methylethylene, 1,3-dimethyltrimethylene, 1-ethylpropylidene, trimethylethylene, isopropylmethylene, 1-methylbutylidene, 2,2-dimethylpropylidene, hexamethylene, 1-ethylbutylidene, 1,2-diethylethylene, 1,3-dimethylbutylidene, ethyltrimethylethylene, heptamethylene, octamethylene, 1,1-cyclopentylidene, 1,1-cyclohexylidene, 1,1-cycloheptylidene, 1,1-cyclooctylidene, benzylidene and 1-phenylethylidene group.

In the copolyesters according to the invention, the radical B contained in the triol units (I) present in the copolyesters can be the same or different. Of these, the radical B in the triol units of the copolyesters according to the invention is preferably an isopropylidene, sulfonyl and/or 1,1-cyclohexylidene group, which leads to good thermal stability of the copolyesters when melting.

In the copolyesters according to the invention, p, q, r, s, t and u in the triol units (I) and triol units (II) are each independently an integer from 1 to 8. The values of p, q, r, s, t and u can therefore be the same or different. It is particularly desirable that p, q, r, s, t and u are each independently an integer of 1 or 2 which leads to good thermal stability of the copolyesters during melting.

Furthermore, in the copolyesters of the invention, it is particularly preferred that the triol units (I) and (II) have the following formulas (IX) and (X), respectively, in view of production costs and ease of production and melt stability of the copolyesters.

It is necessary that the copolyesters of the present invention comprise at least one group of units selected from the triol units (I) and the triol units (II) in an amount of (when both are contained, the total amount thereof) 0.01 to 1 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the above triol units (i.e., at least one group of triol units selected from the triol units (I) and the triol units (II)) constituting the polyesters. In other words, the copolyesters should contain 0.01 to 1 mol of the triol units (I) and/or the triol units (II) based on 100 mol of the sum of the total diol units and these triol units.

When the triol units (I) and/or triol units (II) are contained in an amount of less than 0.01 mol%, the moldability in melt molding such as extrusion blow molding becomes poor, so that, particularly in extrusion blow molding, the extruded parisons sag and collapse badly and never give hollow articles with a good shape. In addition, when the amount is less than 0.01 mol%, the rate of solid-phase polymerization in the production of the copolyesters decreases, thereby reducing their productivity.

On the other hand, if the content of triol units (I) and/or triol units (II) exceeds 1 mol%, the resulting copolyester has too much crosslinked structure and gives rise to gels caused by the crosslinked structure, so that difficulties such as generation of agglomerates and whitening occur in the production of molded articles, which impairs their appearance. In order to prevent gelation, it may be attempted to reduce the degree of polymerization of the copolyesters, but this reduces the level of entanglement between molecules and causes the resulting molded articles to have only insufficient mechanical strength. In addition, if the content of triol units (I) and/or triol units (II) exceeds 1 mol%, the crystallization rate in the production of molded articles becomes too high, so that spherulites are formed and the molded articles turn white, which impairs their appearance. Furthermore, in this case, poor molding may occur and in extrusion blow molding, the blow moldability becomes worse due to the crystallization of the parison.

In the case of the copolyesters (A), it is particularly preferred that the content of triol units (I) and/or triol units (II) is in the range of 0.03 to 0.7 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol units, which provides the resulting copolyesters with a sufficiently high melt viscosity and good melt shape In this case, the resulting molded articles are free from whitening or poor moldability and have excellent mechanical strength, and the copolyester itself has high productivity. From the same viewpoint, it is particularly preferred for the copolyester (B) to have a content of triol units (I) and/or triol units (II) of 0.05 to 0.5 mol% on the same basis.

Of the copolyesters according to the invention, the copolyester (B) which, in addition to the ethylene glycol units, carries as diol units at least one group of units selected from the diol units (III) and the diol units (IV), has good impact resistance.

The copolyester (B) of the invention may contain, together with ethylene glycol units, either one or both of the diol units (III) and diol units (IV), and may contain, as triol units, either one or both of the triol units (I) and triol units (II). More specifically, with regard to the presence of the diol units (III), diol units (IV), triol units (I) and triol units (II), the copolyester (B) of the invention includes the following 9 embodiments, each of which

1. Diol units (III) and triol units (I),

2. Diol units (III) and triol units (II),

3. Diol units (IV) and triol units (I),

4. Diol units (IV) and triol units (II),

5. Diol units (III), diol units (IV) and triol units (I),

6. Diol units (III), diol units (IV) and triol units (II),

7. Diol units (III), triol units (I) and triol units (II),

8. Diol units (IV), triol units (I) and triol units (II),

9. Diol units (III), diol units (IV), triol units (I) and triol units (II).

Of these, the above 1 and 4 are preferred in view of the easiness of production of the polyester (B).

In the diol units (III) and diol units (IV), the residue A is a residue (ethylene group) of the formula -CH₂CH₂- or a residue (1,2-propylene group) of the formula -CH(CH₃)CH₂-. In the copolyester (B) according to the invention and the diol units (III) and/or diol units (IV) and triol units (I) and/or triol units (II) contained therein, all the residues A may be an ethylene group, all the residues A may be a 1,2-propylene group, or part of the residues A may be an ethylene group while the residue is a 1,2-propylene group. Of these cases, it is desirable, in view of the ease of preparation of the copolyester (B) and the production cost, that the residue A in the diol units (III) and/or Diol units (IV) and triol units (I) and/or triol units (II) in the copolyester (B) is the ethylene group.

The residue B in the diol units (III) is a divalent hydrocarbon residue, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-). When the B radical is a divalent hydrocarbon radical, the radical is desirably an alkylene radical or alkylidene radical having 1 to 8 carbon atoms or a divalent aromatic radical. Specific examples of desirable divalent hydrocarbon radicals are the methylene, ethylene, ethylidene, 1,2-propylene, propylidene, trimethylene, isopropylidene, butylidene, ethylethylene, tetramethylene, 1-methylpropylidene, 1,2-dimethylethylene, pentylidene, 1-methylbutylidene, pentamethylene, 1-ethyl-2-methylethylene, 1,3-dimethyltrimethylene, 1-ethylpropylidene, trimethylethylene, isopropylmethylene, 1-methylbutylidene, 2,2-dimethylpropylidene, hexamethylene, 1-ethylbutylidene, 1,2-diethylethylene, 1,3-dimethylbutylidene, ethyltrimethylethylene, heptamethylene, octamethylene, 1,1-cyclopentylidene, 1,1-cyclohexylidene, 1,1-cycloheptylidene, 1,1-cyclooctylidene, benzylidene and 1-phenylethylidene group.

In the copolyester (B) according to the invention, the radical B contained in the diol units (III) and triol units (I) present in the copolyester (B) can be the same or different. Of these, the radical B in the diol units (III) and triol units (I) of the copolyester (B) according to the invention is preferably an isopropylidene, sulfonyl and/or 1,1-cyclohexylidene group, which leads to good thermal stability of the copolyester during melting.

In the copolyester (B) of the invention, j, k, m and n in the diol units (III) and diol units (IV) are each independently an integer from 1 to 8. The values of j, k, m and n can therefore be the same or different. It is particularly desirable that j, k, m and n are each independently an integer of 1 or 2, which guarantees good thermal stability of the copolyesters during melting.

Furthermore, in the copolyester (B) of the present invention, it is particularly preferred that the diol units (III) and diol units (IV) have the following formulas (XI) and (XII), respectively, in view of production costs and ease of production and melt stability of the copolyester (B).

It is necessary that the copolyester (B) of the present invention comprises at least one group of units selected from the diol units (III) and the diol units (IV) in an amount of (when both are contained, the total amount thereof) 1 to 15 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the above triol units (i.e., triol units (I) and/or triol units (II)) constituting the copolyester (B). In other words, the copolyester (B) should contain 1 to 15 mol of the diol units (III) and/or diol units (IV) based on 100 mol of the sum of the total diol units and the above triol units.

When the diol units (III) and/or diol units (IV) are contained in an amount of less than 1 mol%, the rate of solid phase polymerization in the production of copolyester (B) becomes low. Besides, the resulting copolyester (B) has too high a melting point, so that the cycle time in carrying out extrusion blow molding or similar melt molding processes becomes long, thereby reducing the productivity in the production of molded articles.

On the other hand, if the content of diol units (III) and/or diol units (IV) exceeds 15 mol%, the polyester prepolymer which is an intermediate in the production of copolyester (B) has too low a melting point or becomes amorphous, thereby causing such difficulties that chips of the prepolymer stick together in the primary crystallization in the polymerization step or in the solid phase polymerization or it becomes impossible to carry out the solid phase polymerization itself. In addition, the resulting copolyester (B) is noticeably discolored so that molded articles obtained therefrom have a poor color tone.

It is particularly preferred that the content of the diol units (III) and/or diol units (IV) is in the range of 5 to 10 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the above triol units, which can shorten the cycle of melt molding, particularly extrusion blow molding, guarantee good color and mechanical properties such as impact resistance, and ensure high productivity in solid phase polymerization without polyester prepolymer chips sticking together.

The copolyesters of the invention may optionally contain, in addition to the above terephthalic acid units, ethylene glycol units, diol units (III), diol units (IV), triol units (I) and triol units (II), not more than 10 mol%, based on the moles of the total structural units, of structural units derived from other bifunctional compounds. Examples of structural units derived from such bifunctional compounds are those derived from bifunctional groups, for example from aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, bi phenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid and sodium sulfoisophthalate; of aliphatic dicarboxylic acids such as malonic acid, succinic acid, adipic acid, azelaic acid and sebacic acid; of alicyclic dicarboxylic acids such as decalinedicarboxylic acid and cyclohexanedicarboxylic acid; of hydroxycarboxylic acids such as glycolic acid, hydroxyacrylic acid, hydroxypropionic acid, quinic acid, hydroxybenzoic acid and mandelic acid: of aliphatic lactones such as ε-caprolactone; of aliphatic diols such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol and polyethylene glycols; of aromatic diols such as hydroquinone, catechol, naphthalenediol, resorcinol, bisphenol A and bisphenol 5; and alicyclic diols such as cyclohexanedimethanol. Furthermore, the copolyesters according to the invention may optionally contain not more than 0.1%, based on the total structural units constituting them, of units of multifunctional compounds, e.g. polybasic carboxylic acids such as trimellitic acid, trimesic acid and tricarballylic acid; and polyhydric alcohols such as trimethylolpropane and pentaerythritol.

The intrinsic viscosity of the copolyesters of the present invention, which varies according to the type of melt molding used, is desirably in the range of 0.6 to 1.5 dl/g when melt molded, which involves melt extrusion, particularly extrusion blow molding, and more preferably in the range of 0.9 to 1.4 dl/g in view of mechanical strength and appearance as well as productivity in producing molded articles. Particularly, when the intrinsic viscosity is less than 0.6 dl/g, the parisons produced in extrusion blow molding sag considerably, causing poor molding, and further, the resulting molded articles tend to have low mechanical strength.

On the other hand, when the copolyesters have an intrinsic viscosity exceeding 1.5 dl/g, the melt viscosity becomes too high when melting operations accompanying melt extrusion, particularly in extrusion blow molding, are carried out, so that the molded articles in melt extrusion, particularly in extrusion blow molding, tend to produce weld lines and also have a poor appearance. Besides, difficulties in molding occur such as uneven throughput due to high torque in extrusion. In addition, the copolyesters having an intrinsic viscosity exceeding 1.5 dl/g require a long time for their extrusion, so that the productivity of the molded articles is reduced. The above relationship between the intrinsic viscosity of the copolyesters and their moldability and the physical properties of the molded articles obtained therefrom appears particularly pronounced when they are extrusion blow molded. Not limited to the ex However, a similar tendency is observed in melt molding associated with melt extrusion in general, such as extrusion and injection extrusion.

The copolyester (A) of the present invention desirably has a melt viscosity (η₁) at a shear rate of 0.1 rad/s and at a temperature of 270°C of 5 x 10⁴ to 5 x 10⁶ poise. Then, when the copolyester (A) is melt-molded by, for example, extrusion blow molding, it causes little curl-back, thereby almost completely preventing the occurrence of poor molding and considerably suppressing melt fracture, mold swelling and the like. As a result, molded articles having particularly excellent appearance and mechanical properties can be obtained.

The copolyester (A) of the present invention also desirably has a melt viscosity (η₂) at a shear rate of 100 rad/s and at a temperature of 270°C of 5 x 10³ to 5 x 10⁵ poise. Then, when melt-molded by, for example, extrusion blow molding, the copolyester (A) smoothly prevents extrudates such as parisons from being deformed by pulling down or drooping, so that productivity becomes high. In addition, the polyester (A) does not thermally decompose or cause uneven extrusion or occurrence of weld lines.

It is particularly desirable that the copolyester (A) of the present invention not only satisfies the elements of melt viscosity (η1) at a shear rate of 0.1 rad/s and at a temperature of 270°C and melt viscosity (η2) at a shear rate of 100 rad/s and at a temperature of 270°C, but also the following Condition 1:

- 0.7 ? (1/3)log10(?2/?1) ? -0.2 1

By satisfying the above condition 1, the copolyester (A) exhibiting suitable non-Newtonian behavior exhibits a moderately low melt viscosity at high shear rates and a moderately high melt viscosity at low shear rates, thereby having excellent parison moldability when subjected to particularly extrusion blow molding, injection extrusion or similar melt molding.

In order to obtain even better parison formability, it is more preferable that the value (1/3)log₁₀(η₂/η₁) in the above formula 1 is in the range of -0.60 to -0.25. In the above formula 1, the value (1/3)log₁₀(η₂/η₁) can be obtained as the slope of the straight line connecting the two points of the melt viscosities η₁ and η₂ in a double logarithmic graph , where the ordinate represents the melt viscosity and the abscissa represents the shear rate.

The copolyester (B) of the present invention desirably has a melt viscosity (η₃) at a shear rate of 0.1 rad/s and at a temperature of 40°C above the melting point of 5 x 10⁴ to 5 x 10⁶ poise. Then, when melt-molded by, for example, extrusion blow molding, the copolyester (B) causes little curl-back, thereby almost completely preventing the occurrence of poor molding and considerably suppressing melt fracture, mold swelling and the like. As a result, molded articles having particularly excellent appearance and mechanical properties can be obtained.

The copolyester (B) of the present invention also desirably has a melt viscosity (η₄) at a shear rate of 100 rad/s and at a temperature of 40°C above the melting point of 5 x 10³ to 5 x 10⁵ poise. Then, when melt-molded by, for example, extrusion blow molding, the copolyester (B) smoothly prevents extrudates such as parisons from deforming by pulling down or drooping, so that productivity becomes high. In addition, the polyester (B) does not thermally decompose or cause uneven extrusion or occurrence of weld lines.

It is particularly desirable that the copolyester (B) of the present invention not only satisfies the elements of melt viscosity (η3) at a shear rate of 0.1 rad/s and at a temperature of 40°C above the melting point and melt viscosity (η4) at a shear rate of 100 rad/s and at a temperature of 40°C above the melting point, but also the following Condition 2:

- 0.7 ? (1/3)log 10 (η 4 / η 3 ) ? - 0.2 2

By satisfying the above condition 2, the copolyester (B) exhibiting suitable non-Newtonian behavior exhibits a moderately low melt viscosity at high shear rates and a moderately high melt viscosity at low shear rates, thereby having excellent parison moldability when subjected to particularly extrusion blow molding, injection extrusion or similar melt molding.

In order to obtain even better parison formability, it is more preferable that the value (1/3)log₁₀(η₄/η₃) in the above formula 2 is in the range of -0.60 to -0.25. In the above formula 2, the value (1/3)log₁₀(η₄/η₃) can be obtained as the slope of the straight line connecting the two points of the melt viscosities η₃ and η₄ in a double logarithmic graph , where the ordinate represents the melt viscosity and the abscissa represents the shear rate.

It is desirable that the copolyesters of the present invention have a glass transition temperature of at least 60°C. It is more preferred that the glass transition temperature is at least 70°C, which more effectively prevents the formation of glass transitions by extrusion blow molding or similar melt molding shrink. In the case of copolyesters having a glass transition temperature of less than 60ºC, the resulting molded articles, particularly extrusion blow molded articles, sometimes shrink after removal from the molds due to relaxation of residual stress, thereby affecting their appearance.

It is further desirable that the copolyesters of the present invention have a melt flow rate (hereinafter sometimes referred to as "MFR") at a temperature of 40°C above the melting point of 0.3 to 7.5 g/10 min, more preferably 0.5 to 5 g/10 min, from the viewpoint of moldability in melt molding such as extrusion blow molding, uniformity of the molded articles obtained and productivity in molding.

The above copolyesters according to the invention can be produced in a short time and with good productivity by using starting materials consisting essentially of

(1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof,

(2) a diol component consisting essentially of ethylene glycol; or a diol component comprising ethylene glycol and a diol component (VII) of the above formula (VII) and/or a diol component (VIII) of the above formula (VIII) in an amount of 1 to 15 mol% based on the sum of the molar numbers of the total diol units and the mole numbers of the triol component described in item (3) below; and

(3) a triol component containing a triol component (V) of the formula (V) and/or a triol component (VI) of the formula (VI) in an amount of 0.01 to 1 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol component described in this item (3);

esterified or transesterified to produce a polyester prepolymer, and subsequently the polyester prepolymer is polymerized in the solid phase.

The above series of reactions can produce, in the resulting copolyesters, the triol units (I) from the triol component (V) of formula (V), the triol units (II) from the triol component (VI) of formula (VI), the diol units (III) from the diol component (VII) of formula (VII), and the diol units (IV) from the diol component (VIII) of formula (VIII). Consequently, in the above formulas (V) and (VI) or (VII) and (VIII) relating to the triol components or the diol components, respectively, the nature or substance and the desirable examples of the residue A and the residue B and further the details and desirable values for j, k, m, n, p, q, r, s, t and u are as detailed in the above description for the triol units (I), triol units (II), diol units (III) and diol units (IV) with respect to the group A and the group B and j, k, m, n, p, q, r, s, t and u. Preferred concrete examples of the triol components (V) and (VI) are as follows.

First, preferred examples of the triol component (V) used for producing the copolyesters of the present invention are as follows.

Reference No. 1

2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]- propane (hereinafter sometimes referred to as "HEPP")

Reference No. 2

2-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]propane

Reference No. 3

2-[4-(2-Hydroxyethoxy)phenyl]-2-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)-ethoxy]phenyl}propane

Reference No. 4

2-[4-(2-Hydroxyethoxy)phenyl]-2-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-(2-hydroxyethoxy)phenyl}propane

Reference No. 5

2-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-2-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}propane

Reference No. 6

2-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-2-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl} propane

Reference No. 7

[4-(2-Hydroxyethoxy)phenyl]-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]sulfone

Reference No. 8

{4-[2-(2-Hydroxyethoxy)ethoxy]phenyl}-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]sulfone

Reference No. 9

[4-(2-Hydroxyethoxy)phenyl]-{3'-(2-hydroxyethyl)-4'-[2'-(2-hydroxyethoxy)ethoxy]-phenyl}sulfone

Reference No. 10

[4-(2-Hydroxyethoxy)phenyl]-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-(2-hydroxyethoxy)phenyl}sulfone

Reference No. 11

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}sulfone

Reference No. 12

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl} sulfone

Reference No. 13

1-[4-(2-Hydroxyethoxy)phenyl]-1-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]-cyclohexane

Reference No. 14

1-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-1-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]cyclohexane

Reference No. 15

1-[4-(2-Hydroxyethoxy)phenyl]-1-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)-ethoxy]phenyl}cyclohexane

Reference No. 16

1-[4-(2-Hydroxyethoxy)phenyl]-1-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-(2-hydroxyethoxy)phenyl}cyclohexane

Reference No. 17

1-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-1-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}cyclohexane

Reference No. 18

1-{4-[2-(2-Hydroxyethoxy)ethoxy]phenyl}-1-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl} cyclohexane

Reference No. 19

[4-(2-Hydroxyethoxy)phenyl]-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]ether

Reference No. 20

{4-[2-(2-Hydroxyethoxy)ethoxy]phenyl}-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)-phenyl]ether

Reference No. 21

[4-(2-Hydroxyethoxy)phenyl]-{3'-(2-hydroxyethyl)-4'-[2'-(2-hydroxyethoxy)ethoxy]-phenyl}ether

Reference No. 22

[4-(2-Hydroxyethoxy)phenyl]-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-(2-hydroxyethoxy)phenyl}ether

Reference No. 23

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}ether

Reference No. 24

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}ether

Reference No. 25

[4-(2-Hydroxyethoxy)phenyl]-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]ketone

Reference No. 26

{4-[2-(2-Hydroxyethoxy)ethoxy]phenyl}-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]ketone

Reference No. 27

[4-(2-Hydroxyethoxy)phenyl]-{3'-(2-hydroxyethyl)-4'-[2'-(2-hydroxyethoxy)ethoxy]-phenyl}ketone

Reference No. 28

[4-(2-Hydroxyethoxy)phenyl]-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-(2-hydroxyethoxy)phenyl}ketone

Reference No. 29

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}ketone

Reference No. 30

{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]phenyl}ketone

Reference No. 31

4-(2-Hydroxyethoxy)-3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)biphenyl

Reference No. 32

4-[2-(2-Hydroxyethoxy)ethoxy]-3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)biphenyl

Reference No. 33

4-(2-Hydroxyethoxy)-3'-(2-hydroxyethyl)-4'-[2'-(2-hydroxyethoxy)ethoxy]biphenyl

Reference No. 34

4-(2-Hydroxyethoxy)-{3'-[2-(2-hydroxyethoxy)ethoxy]-4'-(2-hydroxyethoxy)phenyl}-biphenyl

Reference No. 35

4-[2-(2-Hydroxyethoxy)ethoxy]-3'-(2-hydroxyethyl)-4'-[2-(2-hydroxyethoxy)ethoxy]-biphenyl

Reference No. 36

4-[2-(2-Hydroxyethoxy)ethoxy]-3'-[2-(2-hydroxyethoxy)ethyl]-4'-[2-(2-hydroxyethoxy)ethoxy]biphenyl

Reference No. 37

2-{4-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl}-2-{3'-(2-hydroxyethoxy)-4'-{2-[2-(2-hydroxyethoxy)ethoxy ]ethoxy}phenyl}propane

Reference No. 38

2-{4-{2-[2-(2-Hydroxyethoxy)ethoxy]ethoxy}phenyl}-2-{3'-(2-hydroxyethyl)-4'- {2-{2-[2-(2- hydroxyethoxy)ethoxy]ethoxy}ethoxy}phenyl}propane

Reference No. 39

2-{4-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}phenyl}-2-{3'-[2-(2-hydroxyethoxy)ethyl]- 4'-phenyl}-phenyl}-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}-ethoxy}phenyl}propane

Reference No. 40

{4-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl}-{3'-[2-(2-hydroxyethoxy)-ethyl]-4'-{2-[2-(2-hydroxyethoxy)-ethyl]-4'-{2-[2-(2-hydroxyethoxy). )ethoxy]ethoxy}phenyl}sulfone

Reference No. 41

{4-{2-[2-(2-Hydroxyethoxy)ethoxy]ethoxy}phenyl}-{3'-[2-(2-hydroxyethoxy)ethyl]- 4'-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}phenyl}sulfone

Reference No. 42

{4-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}phenyl}-{3'-{2-{2-[2-(2-hydroxyethoxy)ethoxy ]ethoxy]ethyl}-4'-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]-ethoxy}ethoxy}ethoxy}phenyl}sulfone

Reference No. 43

{4-{2-[2-(2-Hydroxyethoxy)ethoxy]ethoxy}phenyl}-{3'-{2-{2-[2-(2-hydroxyethoxy)-ethoxy]ethoxy}ethyl}-4'- {2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl}ether

Reference No. 44

{4-{2-{2-{2-[2-(2-Hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}phenyl}-{3'- {2-{2-{2-[2-(2- hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethyl}-4'-{2-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}phenyl}ether

Reference No. 45

{4-{2-[2-(2-Hydroxyethoxy)ethoxy]ethoxy}phenyl}- {3'-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethyl} -4'-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl}-ketone

Reference No. 46

{4-[2-(2-Hydroxyethoxy)ethoxy]phenyl}-{3'-[2-(2-hydroxyethoxy)ethyl]-4'-{2-{2-{2-[2-(2-hydroxyethoxy). )ethoxy]ethoxy}ethoxy}ethoxy}phenyl}ketone

Reference No. 47

4-(2-Hydroxyethoxy)-3'-(2-hydroxyethyl)-4'-{2-[2-(2-hydroxyethoxy)ethoxy]-ethoxy}biphenyl

Reference No. 48

4-{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}-3'-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy }-4'-[2-(2-hydroxyethoxy)ethoxy]biphenyl

Among them, in view of cost and ease of preparation, melt stability of the resulting copolyesters and similar factors, 2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]propane is preferably used as the triol component (V).

Preferred examples of the triol component (VI) used for preparing the copolyesters of the present invention are as follows.

Reference 49

1,4-Bis(2-hydroxyethoxy)-2-(2-hydroxyethyl)benzene

Reference No. 50

1,4-Bis(2-hydroxyethoxy)-2-[2-(2-hydroxyethoxy)ethyl]benzene

Reference No. 51

1-(2-Hydroxyethoxy)-2-(2-hydroxyethyl)-4-[2-(2-hydroxyethoxy)ethoxy]benzene

Reference No. 52

1,4-Bis[2-(2-hydroxyethoxy)ethoxy]-2-(2-hydroxyethyl)benzene

Reference No. 53

1-(2-Hydroxyethoxy)-2-[2-(2-hydroxyethoxy)ethyl]-4-[2-(2-hydroxyethoxy)ethoxy]-benzene

Reference No. 54

1,4-Bis[2-(2-hydroxyethoxy)ethoxy]-2-[2-(2-hydroxyethoxy)ethyl]benzene

Reference No. 55

1,4-Bis{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}-(2-hydroxyethyl)benzene

Reference No. 56

1-[2-(2-Hydroxyethoxy)ethyl]-2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}-5-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy). }benzene

Reference No. 57

1,4-Bis{2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}ethoxy}-2-{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy }ethoxy}ethyl}benzene.

Among them, in view of cost and ease of preparation, melt stability of the resulting copolyesters and similar factors, 1,4-bis(2-hydroxyethoxy)-2-(2-hydroxyethyl)benzene is preferably used as the triol component (VI).

Preferred examples of the diol component (VII) used to prepare the copolyester (B) according to the invention are 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, 2-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-2-[4'-(2-hydroxyethoxy)phenyl]propane, 2,2-bis{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}propane, bis[4-(2-hydroxyethoxy)phenyl]sulfone,{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-[4'-(2-hydroxyethoxy)phenyl]sulfone, bis{4-[2- (2-hydroxyethoxy)ethoxy]phenyl}sulfone, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 1-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-1-(4'-(2-hydroxyethoxy)phenyl]cyclohexane and 1,1-bis(4-[2-(2-hydroxyethoxy)ethoxy]phenyl}cyclohexane.

Among them, in view of cost and ease of production of the copolyester (B), melt stability of the resulting copolyester (B) and the like, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane is preferably used as the diol component (VII).

Preferred examples of the diol component (VIII) used for preparing the copolyester (B) of the invention are 1,4-bis(2-hydroxyethoxy)benzene, 1-(2-hydroxyethoxy)-4-[2-(2-hydroxyethoxy)ethoxy]benzene and 1,4-bis[2-(2-hydroxyethoxy)ethoxy]benzene.

Among them, in view of cost and ease of production of the copolyester (B), melt stability of the resulting copolyester (B) and the like, 1,4-bis(2-hydroxyethoxy)benzene is preferably used as the diol component (VIII).

In preparing the copolyesters of the present invention, components other than the above terephthalic acid component, ethylene glycol, diol component (VII), diol component (VIII), triol component (V) and triol component (VI) may optionally be used in combination as long as the amount thereof is not more than 10 mol% based on the moles of the total reaction components. Examples of such other components are, as indicated in the above description of other copolymerization units which may be contained in the copolyesters of the present invention, bifunctional groups, e.g., aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenyl ketone dicarboxylic acid, sodium sulfoisophthalate and ester-forming derivatives of the above; aliphatic dicarboxylic acids such as malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid and ester-forming derivatives of the above; alicyclic dicarboxylic acids such as decalindicarboxylic acid, cyclohexanedicarboxylic acid and ester-forming derivatives of the above; hydroxycarboxylic acids such as glycolic acid, hydroxyacrylic acid, hydroxypropionic acid, chinova acid, hydroxybenzoic acid, mandelic acid and ester-forming derivatives of the above; aliphatic lactones such as ε-caprolactone; aliphatic diols such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol and polyethylene glycols; aromatic diols such as hydroquinone, catechol, naphthalenediol, resorcinol, bisphenol A and bisphenol S; and alicyclic diols such as cyclohexanedimethanol. Furthermore, not more than 0.1%, based on the total reaction components, of multifunctional compounds, e.g. polyvalent carboxylic acids such as trimellitic acid, trimesic acid, tricarballylic acid or ester-forming derivatives of the above; and polyvalent alcohols such as trimethylolpropane and pentaerythritol may optionally be used.

In the preparation of the copolyester (A), as described above, a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof is esterified or transesterified with a diol component consisting essentially of ethylene glycol and a triol component [i.e., triol component (V) and/or triol component (VI)] to form a compound having a low degree of polymerization. It is recommended that, on this occasion, the reaction components be mixed so that the molar ratio of (total diol components):(total dicarboxylic acid components) becomes 1.1:1 to 1.5:1 and that the molar ratio of (triol component):(total dicarboxylic acid components) is 0.01:100 to 1:100.

In the preparation of the copolyester (B), as described above, a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof is esterified or transesterified with a diol component consisting essentially of ethylene glycol and further containing a diol component (VII) and/or diol component (VIII) and a triol component [i.e., triol component (V) and/or triol component (VI)], thereby forming a compound having a low degree of polymerization. It is recommended on this occasion to mix the reaction components so that the molar ratio of (total diol components):(total dicarboxylic acid components) becomes 1.1:1 to 1.5:1 and that the molar ratio of (triol component):(total dicarboxylic acid components) becomes 0.01:100 to 1:100.

It is also recommended that the above esterification or transesterification is generally carried out under normal pressure up to an absolute pressure of about 3 kg/cm² and at a temperature of 230 to 280°C while distilling off generated water or alcohol. After the reaction, additives such as a polycondensation catalyst and a discoloration inhibitor are optionally added and then melt polycondensation is generally carried out under a reduced pressure of not more than 5 mmHg and at a temperature of 200 to 280°C until a polyester prepolymer having the desired viscosity is obtained. The polyester prepolymer on this occasion desirably has an intrinsic viscosity of 0.40 to 0.80 dl/g and an MFR exceeding 15.0 g/10 min in view of handleability and the like.

When a polycondensation catalyst is used for the above melt polycondensation, the catalyst may be any one generally used for producing polyesters. Examples of the catalyst are antimony compounds such as antimony oxide; germanium compounds such as germanium oxide; titanium compounds such as tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium and tetrabutoxytitanium; and tin compounds such as di-n-butyltin dilaurate, di-n-butyltin oxide and dibutyltin diacetate. These catalysts may be used alone or in combination of two or more. When a polycondensation catalyst is used, the amount thereof is desirably in the range of 0.002 to 0.8% by weight based on the weight of the dicarboxylic acid component.

When a discoloration inhibitor is used, phosphorus compounds such as phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate and triphenyl phosphate can be used. These phosphorus compounds can be used alone or in combination of two or more. When using a discoloration inhibitor comprising any of the above phosphorus compounds, the amount thereof is desirably in the range of 0.001 to 0.5 wt% based on the weight of the dicarboxylic acid component.

In order to suppress discoloration of the copolyesters due to thermal decomposition, it is recommended to add a manganese compound such as manganese acetate in an amount of 0.001 to 0.5 wt% based on the weight of the dicarboxylic acid component, more preferably 0.05 to 0.3 wt% on the same basis.

It is also desirable to carry out the above esterification or transesterification and/or melt polycondensation in the presence of an agent that suppresses the formation of diethylene glycol byproducts, for example, tetraalkylammonium hydroxides such as tetraethylammonium hydroxide and organic amines such as triethanolamine and triethylamine.

Then, the polyester prepolymer obtained by the above polycondensation is formed into chips or pellets having a cubic, cylindrical or any optional shape, which, after being predried at a temperature generally not higher than 190°C, are polymerized in solid phase until the intrinsic viscosity, MFR and similar indices reach the desired values, thereby giving the desired copolyester. The solid phase polymerization is desirably carried out under vacuum or reduced pressure or under an atmosphere of inert gas such as nitrogen. During the solid phase polymerization, it is desirable to agitate the chips or pellets of the polyester prepolymer by suitable means such as a drum method or a gas fluidized bed method so that they do not stick together. The solid phase polymerization is desirably carried out generally at a temperature of 180 to 240°C, more preferably 210 to 240°C. Further, from the viewpoint of preventing the chips or pellets from sticking together, it is recommended to set the temperature for the solid phase polymerization within the above range at least 15°C, preferably at least 20°C lower than the melting point of the copolyester to be produced (the one finally obtained). The solid phase polymerization is desirably carried out generally for about 5 to 40 hours from the viewpoint of productivity and the like.

Carrying out the above series of processes can give the copolyesters of the invention in a short period of time and with high productivity.

The copolyesters of the present invention can be molded into various molded articles by extrusion blow molding, injection extrusion molding, extrusion, injection molding or similar melt molding methods with good moldability. The molded articles obtained by these melt molding methods can give molded articles having excellent dimensional stability, transparency, heat resistance, moisture resistance, chemical resistance and similar properties with good productivity and smoothly.

The copolyesters of the present invention have high melt viscosity and melt viscosity properties which are particularly suitable for melt molding processes involving melt extrusion processes, particularly extrusion blow molding, among the above melt molding processes. In extrusion blow molding with the copolyesters of the present invention, the extruded parisons have a good settling property so that the settling time is kept within an appropriate range and the parisons have a uniform diameter. Besides, good blow moldability is achieved without causing difficulty in molding, whereby hollow moldings having good shape and dimensional stability are produced smoothly and with good productivity. The resulting hollow moldings can give extruded blow molded articles having excellent transparency, heat resistance, moisture resistance, chemical resistance and the like.

Furthermore, the copolyesters according to the invention with the above features are suitably used to produce large hollow molded parts over relatively long parisons with a length of at least 20 cm.

Melt molding of the copolyesters of the present invention can be carried out following conventional procedures for any of the melt molding methods generally used for thermoplastic resins, e.g., extrusion blow molding, injection extrusion molding, extrusion molding and injection molding, and is not particularly limited in terms of specific content or conditions of the procedure. In particular, in extrusion blow molding of the copolyesters of the present invention, the manner of extrusion blow molding is not particularly limited. That is, in the same manner as in the known extrusion blow molding, the copolyesters of the present invention can be melt extruded into cylindrical parisons, which are placed in a blow molding die while in a softened state, and then air or similar gases are blown into the die, thereby inflating the parisons into desired hollow shapes defined by the shape of the die cavity. In this case, in view of the moldability, it is desirable to set the melt extrusion temperature within a range of (melting point of the copolyester + 10ºC) to (melting point of the copolyester + 70ºC).

The molded articles of the present invention may be of any shape without particular limitation, and may take the shape of, for example, a hollow article, a pipe, a plate, a sheet, a film, a rod, and a mold according to the respective use. The molded articles may be of any size without particular limitation. Among them, the present invention is particularly suitably applied to hollow articles obtained by extrusion blow molding.

Furthermore, the molded articles obtained from the copolyesters of the invention can be molded from the copolyesters alone, or can be in the form of laminates with other plastics, metals, fibers, fabrics or similar other materials, or can be in a form other than the laminates in combination with the above other materials. In particular, when the molded articles of the invention are extruded articles, they can be molded into single-layer hollow articles (e.g. hollow containers) comprising only the copolyesters of the invention, or into multi-layer hollow articles produced from the copolyesters of the invention in combination with other plastics, such as polyethylene, polypropylene, ethylene-vinyl alcohol copolymer or polyethylene terephthalate (PET). More specifically, three-layer bottles having a structure of PET layer/copolyester layer/PET layer and five-layer bottles having PET layer/copolyester layer/PET layer/copolyester layer/PET layer may be mentioned. However, the molded articles of the present invention are not limited to these examples.

The copolyesters according to the invention may optionally contain other thermoplastic resins and various additives conventionally used for polyester resins in general substances, e.g. colorants such as dyes and pigments, stabilizers such as UV absorbers, antistatic agents, flame retardants, flame retardant aids, lubricants, plasticizers and inorganic fillers.

The aromatic triols of general formula (V) can be prepared by introducing a suitable bisphenol into an airtight vessel and treating it with an excess amount of alkylene oxide under pressure and in the presence of a catalytic amount of a base. The reaction temperature is preferably in the range of 70 to 250°C, more preferably in the range of 80 to 230°C. The reaction time, which depends on the reaction temperature, is generally in the range of about 5 to about 10 hours. The alkylene oxide used is preferably present in an amount of 4 to 15 molar equivalents based on the bisphenol. The reaction is desirably carried out in a solvent.

Examples of the bisphenol used in the above reaction, which suitably correspond to the general formula (I), are bisphenol A (4,4'-isopropylidenediphenol), bisphenol S [bis(4-hydroxyphenyl)sulfone], bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)ketone and 4,4'-dihydroxybiphenyl. Examples of usable alkylene oxides are ethylene oxide and propylene oxide. Examples of the base acting as a reaction catalyst are inorganic bases such as potassium carbonate, sodium carbonate, sodium methylate, sodium ethylate, sodium hydroxide and potassium hydroxide, and amine-based bases such as triethylamine, trimethylamine and tributylamine.

The aromatic triols of general formula (VI) can be prepared by following the same procedure in the above preparation process for the aromatic triols of general formula (V), except that the bisphenol is changed to a hydroquinone.

The aromatic triols of the general formula (VI) can also be prepared by condensing a starting material 2,5-dihydroxyphenylacetic acid (homogentisic acid) with an ethylene halohydrin or propylene halohydrin in the presence of a basic catalyst and reducing the carboxyl group with a reducing agent using a known method.

Examples of the ethylene halohydrin and propylene halohydrin used in the above reaction are ethylene chlorohydrin, ethylene bromohydrin, propylene chlorohydrin and propylene bromohydrin, of which ethylene bromohydrin and propylene bromohydrin are preferred in view of the reactivity. The same bases as those used for preparing the aromatic triols of the general formula (V) are also applicable here. Examples of the reducing agent are metal hydrides, e.g. aluminum lithium hydride, aluminum tri(t-butoxy)- hydride and sodium borohydride, of which aluminium lithium hydride is preferred in terms of reactivity and economic efficiency.

The triols thus obtained are optionally purified by any known method, such as recrystallization or column chromatography, thereby achieving higher purity.

The aromatic triols are useful as crosslinking agents and resin modifiers. For example, in the preparation of a polycondensed polymer such as polyesters, polyurethanes or polycarbonates, premixing an aromatic triol of the present invention as a copolymerization monomer into the starting material mixture and polycondensing the resulting mixture can provide crosslinkable polymers in which the three hydroxyl groups contained in the aromatic triol form an ester bond, urethane bond or carbonate bond. Modification of polyesters with an aromatic triol of the present invention enables the resulting polyesters to have good extrusion blowability.

EXAMPLES

Other features of the invention will become more apparent in the course of the detailed descriptions of the illustrated embodiments, which are given to illustrate the invention and are not intended to limit it. In the examples and comparative examples that follow, the determination of the structure and purity of the aromatic triols, the content of each of the structural units and the properties of the polyesters (copolyesters or homopolyesters), as well as the evaluations of the sagging tendency and blow moldability of the parisons during extrusion blow molding of the polyesters and the transparency and impact resistance of the molded articles (bottles) obtained by extrusion blow molding were carried out according to the following methods.

(1) Structure of the aromatic triol

Identified by 500 MHz NMR (manufactured by JEOL) spectrometry using deuterated chloroform as a solvent. In the examples, the values of chemical shift, signal shape and number of protons read from the NMR diagram are given.

(2) Purity of the aromatic triol

Determined by calculating the ratio between the peak area of the compound sample and the total peak area present on the chromatogram obtained by liquid chromatography using a mixed solvent of methanol/water as the mobile phase.

For liquid chromatography, System Controller SCL-6B, Chromatopack C-R4AX, an ultraviolet and visible spectrophotometer SPE-6A (all manufactured by Shimadzu Corporation) and Shim-Pack CLC-ODS (M) as a column (manufactured by Shimadzu Corporation, inner diameter 4.6 mm x 250 mm) were used. The detection wavelength was set to 254 nm.

(3) Content of each structural unit in polyester

Methanolysis was performed on the polyester sample and the structural components were separated by high performance liquid chromatography. The resulting components were each quantified by infrared absorption (IR) spectrometry, which gave the content of each component. The content values were identified by 1H NMR spectrometry in deuterated trifluoroacetic acid as the solvent.

(4) Intrinsic viscosity of polyester

Determined by measuring a 1/1 solvent mixture by weight of phenol and tetrachloroethane with an Ubbelohde viscometer (HRK-3, manufactured by Hayashi Seisakusho) at 30ºC.

(5) Melt index (MFR) of the prepolymer or polyester

Measured with Melt Indexer L244 (manufactured by Takara Kogyo KK). Specifically, a cylinder with an inner diameter of 9.5 mm and a length of 162 mm was filled with chips of a sample of the prepolymer or polyester (final product) which were melted at 270ºC. The melt was uniformly loaded with a plunger weighing 2160 g with a diameter of 9.48 mm, and the outflow rate (g/10 min) of the prepolymer or polyester through an orifice with a diameter of 2.1 mm was measured and taken as the melt index.

(6) Melt viscosities (η1, η2, η3 and η4) of polyester

The melt viscosity at a shear rate of 0.1 rad/s (η1 or η3) at a temperature of 270°C or (melting point + 40°C) and that at a shear rate of 100 rad/s (η2 or η4) at a temperature of 270°C or (melting point + 40°C) were dynamically measured with a mechanical spectrometer (RMS-800, manufactured by Reometrics Co.).

(7) Glass transition temperature (Tg) and melting point (Tm) of polyester

Measured according to JIS K7121 using a differential scanning calorimeter (DSC) with a thermal analysis system (Mettler TA3000) at a rate of 10 ºC/min.

(8) Sinking tendency of the parison during extrusion blow molding (i) Sinking time (s) of the parison

The sample was extruded into a cylindrical parison through an annular opening at an extrusion temperature of 270ºC with an extrusion blow molding machine (hollow molding machine, type TB-ST 6P, manufactured by Suzuki Iron Works). The cylindrical parison was cut and bottom-shaped by pinching with a blow mold while it was in the softened state, and the sections were then blow-molded into bottles (designed capacity: 1000 ml, design wall thickness: 0.4 mm) for soft drinks. The above extrusion blow molding machine used here was designed to pinch and blow with a mold at a time when the parison had sunk by 25 cm. The time required for 25 cm of sunk was measured accordingly and taken as the sunk time.

With the extrusion blow molding machine used here, settling times within a range of 10 to 25 seconds showed good moldability, and those particularly within a range of 15 to 25 seconds showed even better moldability. Settling times of less than 10 seconds, which means bad settling, cause the parison to take on an uneven shape, and such a parison after blowing becomes defective with a large thickness distribution, becomes impossible to insert into blow molds, and causes clogging at its hollow part. On the other hand, if the settling time exceeds 25 seconds, the productivity of the molded parts (bottles) decreases, and the polyester having too high a melt viscosity cannot be blown uniformly. Furthermore, in this case, non-bonding at the pinch-off part of the bottles, generation of weld lines, and breakage of the molding machine due to increased torque may occur.

(ii) Difference between the maximum and minimum diameter of the parison

A polyester sample was extruded into a cylindrical parison by the above extrusion blow molding machine at a temperature of 270ºC, and the parison was measured for its maximum diameter (outer diameter) and minimum diameter (inner diameter) when its length reached 25 cm, and the difference was obtained.

The ring-shaped molding die of the above extrusion blow molding machine used here was 3.5 cm. The parison extruded thereby tends to become thinner as it moves away from the mold due to the sinking caused by its own weight. A difference between the maximum and minimum diameters of a parison generally ensures a smooth extrusion blow molding operation. On the other hand, if the difference exceeds 1 cm, the parison after blowing will produce unevenness in thickness, thereby generating defects, or in extreme cases, it will clog and become unblowable.

(iii) Overall assessment of the sinking tendency of the parison

The overall evaluation of the sinking tendency of the parison was carried out according to the criteria shown in Table 1 below regarding the sinking time, the difference between the maximum and minimum diameter of the parison and the productivity of the bottles. On this occasion, the productivity of the bottles was evaluated as good in terms of cost factor if at least 120 bottles with less than 10 defective ones per 100 could be produced. Here, defective means that at least one difficulty occurred, selected from:

a) the extruded parison cannot be placed into the blow mold due to sinking;

b) the bucket becomes clogged at its hollow part;

c) non-bonding at the pinch-off part due to high viscosity; and

d) Deformation or breakage of the bottle due to uneven blowing.

Table 1 Criteria for the overall assessment of the tendency of the parison to sink

O (good): meets all of the following conditions

(a) Sinking time is in the range of 15 to 25 seconds.

(b) Difference between maximum and minimum diameter of the parison is not more than 1 cm.

(c) Bottle production is at least 120 bottles per hour and less than 10 bottles per 100 bottles are defective.

(borderline): satisfies any of the following conditions

(a) Descent time is at least 10 seconds and less than 15 seconds or is more than 25 seconds and not more than 60 seconds.

(b) Difference between maximum and minimum diameter of the parison is more than 1 cm and not more than 2 cm.

(c) Bottle production is at least 60 and less than 120 units per hour and at least 10 and less than 30 bottles per 100 bottles are defective.

x (bad): satisfies any of the following conditions

(a) Descent time is less than 10 seconds or exceeds 60 seconds.

(b) Difference between maximum and minimum diameter of the parison exceeds 2 cm.

(c) Bottle production is less than 60 bottles per hour and at least 30 bottles per 100 bottles are defective.

(9) Blow moldability in extrusion blow molding (i) Average wall thickness of the bottle

A bottle obtained by molding was divided into 10 pieces from top to bottom, each of which was then divided into 4 pieces at equal distances in the direction of the circumference of the bottle. The wall thicknesses of the 40 pieces were measured and the average of 40 measurements was calculated. The average wall thickness is desirably from the point of view of appearance, tactility and bottle strength in the range of 0.25 to 0.55 mm.

(ii) Inequality in the thickness of the bottle

From the wall thicknesses of the parts of the hook body obtained in the above measurement (i), the difference between the maximum and minimum thickness was obtained for evaluation. The difference in thickness is desirably less than 0.15 mm, otherwise very thin and/or broken parts will be formed so that the appearance and/or tactility will be poor.

(iii) Overall assessment of blow moldability

Conducted according to the criteria shown in Table 2 below.

Table 2 Overall evaluation criteria for blow moldability

O (good): Average wall thickness is in the range of 0.25 to 0.55 mm and thickness unevenness is less than 0.15 mm.

x (poor): Average wall thickness is less than 0.25 mm or exceeds 0.55 mm or inequality in thickness is at least 0.15 mm.

(10) Transparency of the bottle (i) Turbidity value

The bottle body was divided into 6 pieces from the top center to the bottom, each of which was then divided into 4 pieces in the circumferential direction to make 24 pieces. These were tested for the haze value on each piece using an integrating sphere type light transmittance and total light reflectance tester (type SEP-HS 30D-R, manufactured by Nihon Seimitsu Kogaku KK). The average of 24 measurements was taken as the haze value of the bottle. If the haze value exceeds 8, the transparency becomes poor due to whitening caused by the formation of spherulites or light scattering by gel-like agglomerates. The haze value is desirably not more than 4, which ensures good transparency.

(ii) b-value

The bottle body was cut into small pieces (square pieces of 1 cm x 1 cm) which were measured by a color difference meter (SM-4, manufactured by Suga Instruments KK) using the reflection method. If the b value exceeds 8, the bottle shows a yellowish tint and becomes poor in appearance. In terms of color tone, the b value is desirably not more than 4.

(iii) Overall assessment of bottle transparency

Conducted according to the evaluation criteria shown in Table 3 below.

Table 3 Overall evaluation criteria for bottle transparency

O (good): turbidity value is not more than 4 and b-value is not more than 4.

Δ (borderline): turbidity value exceeds 4 but not more than 8 or b-value exceeds 4 but not more than 8.

x (poor): turbidity value exceeds 8 or b-value exceeds 8.

(11) Impact resistance of the bottle

A sample bottle was filled with distilled water and closed by fitting a stopper. After standing for 24 hours at a temperature of 0ºC, the bottle was dropped straight down onto a flat concrete floor from a height of 50 cm. This test was repeated five times with the same bottle and the results were evaluated according to the criteria shown in Table 4 below.

Table 4 Evaluation criteria for the impact resistance of the bottle

O (good): After 5 tests, no cracks or splits occurred.

(marginal): Although no cracks or splits formed after the first test, they did form in any of the second through the fifth tests.

x (poor): Cracks or splits appeared after the first test.

Example 1 (Synthesis of HEPP)

An airtight reaction vessel was charged with bisphenol A (114 parts by weight, 0.5 mol) as a bisphenol starting material, to which 70 parts of toluene and triethylamine (1.0 part by weight, 0.01 mol) were added. After the air in the vessel was replaced with nitrogen at a pressure of 0.7 kg/cm2, ethylene oxide (110 parts by weight, 2.5 mol) was added and the reaction was effected for 5 hours while the temperature was raised from 80°C to 210°C. The reaction was further continued at 200°C for 2 hours. The reaction mixture was allowed to cool and the pressure was reduced, and then hydrochloric acid (50 parts by weight) was added. The resulting reaction mixture was concentrated and isolated and purified by column chromatography, yielding 23.4 parts by weight of HEPP (yield based on bisphenol: 13%).

¹H-NMR (CDCl₃) δ:

1.67 (s, CH3 , 3H), 1.68 (s, CH3 , 3H), 2.40 (b, OH, 1H), 2.88 (t, CH2 , 2H), 3.77 (t, CH2 , 2H), 3.90 (m, CH2 , 4H), 4.10 (m, CH2 , 4H), 6.70-7.15 (m, aromatic ring, 7H)

Example 2 (Synthesis of the compound of reference no. 7) and Example 3 (Synthesis of the compound of reference no. 49)

Example 1 was repeated except that the kind and amount of the raw material compound were changed as shown in Table 5, thereby obtaining aromatic triols corresponding to the raw materials. The results are also shown in Table 5.

Connection of reference no. 7

¹H-NMR (CDCl₃) δ:

2.35 (b, OH, 1H), 2.88 (t, CH2 , 2H), 3.76 (t, CH2 , 2H), 3.92 (m, CH2 , 4H), 4.15 (m, CH2 , 4H), 6.60-7.18 (m, aromatic ring, 7H)

Connection of reference no. 49

¹H-NMR (CDCl₃) δ:

1.22 (t, OH, 1H), 1.54 (m, OH, 1H), 2.95 (t, CH2 , 2H), 3.60 (m, OH, 1H), 3.87 (t , CH2 , 2H), 3.88 (m, CH2 , 4H), 4.05 (m, CH2 , 4H), 6.75-7.00 (m, aromatic ring, 3H)

Example 4 (Synthesis of the compound of reference no. 49)

Homogentisic acid (84.1 parts by weight, 0.5 mol) was dissolved in 100 parts by weight of acetone, and 150 parts by weight of potassium carbonate was added to the solution. To the stirred reaction mixture was carefully added ethylene bromohydrin (189 parts by weight, 1.5 mol), and the resulting mixture was heated to 60°C to cause reaction for 5 hours. From the obtained reaction mixture, potassium carbonate was removed by filtration. After the filtrate was thickened, it was purified by column chromatography to give a condensate of homogentisic acid and ethylene bromohydrin (purity 99.0%). The condensate was dissolved in 200 parts by weight of anhydrous tetrahydrofuran, and 300 ml of aluminum lithium hydride (1 mol/L solution in tetrahydrofuran) was added dropwise with stirring at -50°C. While allowing the reaction temperature to rise to near room temperature, reaction was carried out for 5 hours. Thereafter, 300 parts by weight of methanol was added to the reaction mixture to remove unreacted aluminum lithium hydride. A large excess of diethyl ether and water were added to the reaction mixture, and the organic phase was concentrated. The resulting mixture was isolated and purified by column chromatography to give 110.1 parts by weight of the compound of Reference No. 49 (yield based on homogentisic acid: 91%). The results are shown in Table 5.

¹H-NMR (CDCl₃) δ:

1.21 (t, OH, 1H), 1.57 (m, OH, 1H), 2.95 (t, CH2 , 2H), 3.67 (m, OH, 1H), 3.88 (m , CH2 , 2H), 3.88 (m, CH2 , 4H), 4.03 (m, CH2 , 4H), 6.75-7.00 (m, aromatic ring, 3H) Table 5

Example 5

(1) From 100 parts by weight of terephthalic acid, 44.83 parts by weight of ethylene glycol and 0.108 parts by weight of 2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]propane (HEPP) of the following formula (XIII)

A slurry was prepared. To the slurry were added 0.020 parts by weight of germanium dioxide, 0.015 parts by weight of phosphoric acid, 0.015 parts by weight of manganese acetate and 0.015 parts by weight of tetraethylammonium hydroxide. The resulting slurry was heated under pressure (absolute pressure: 2.5 kg/cm²) at a temperature of 250°C to conduct esterification to an esterification ratio of 95%, thereby preparing a compound having a low degree of polymerization. The compound thus obtained was melt-polycondensed under reduced pressure of 1 mmHg and at a temperature of 270°C to obtain a copolyester prepolymer having an intrinsic viscosity of 0.70 dl/g. The prepolymer was extruded through a die to form a strand, which was then cut into cylindrical chips (diameter: 2.5 mm, length: 3.5 mm). The prepolymer had an MFR of 35 g/10 min.

The copolyester prepolymer chips thus obtained, after being predried at a temperature of 150 °C for 5 hours, were solid-phase polymerized under a reduced pressure of 0.1 mmHg at 225 °C (28 °C lower than the melting point) for 31 hours to give a high molecular weight copolyester.

(2) The copolymer obtained in the above (1) was examined for the content of each structural unit by the methods described above. The content of terephthalic acid units, ethylene glycol units, HEPP units or diethylene glycol units was as shown in Table 7.

(3) The copolymer obtained in the above (1) was tested for physical properties according to the above-described methods, whereby, as shown in Table 7 below, it had an intrinsic viscosity of 1.25 dl/g, an MFR at 270°C of 2.4 g/10 min, and melt viscosities at the same temperature and at a shear rate of 0.1 rad/s (η1) and at a shear rate of 100 rad/s (η2) of 1.47 x 105 poise and 2.30 x 104 poise, respectively, resulting in a value of (1/3)log10(η2/η1) of -0.27.

The copolyester was further tested for Tg and Tm by the procedure described above, which were found to be 78°C and 235°C, respectively, as shown in Table 7 below.

(4) The copolyester was extrusion blow-molded into bottles (designed capacity: 1000 ml, design wall thickness: 0.4 mm) using an extrusion blow molding machine (hollow molding machine TB-ST 6P, manufactured by Suzuki Iron Works). According to the procedures described above, the obtained parison was tested for sagging tendency and blow moldability, and the bottles were tested for transparency, to obtain the results shown in Table 10 below.

Examples 6 and 7

Example 5 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of the solid phase polymerization were changed as shown in Table 7 below to carry out esterification, melt polycondensation and solid phase polymerization to prepare copolyesters. The obtained copolyesters were similarly tested for the content of structural units and physical properties. The results are shown in Table 7 below.

The copolyesters obtained in these Examples 6 and 7 were extrusion-blown into bottles in the same manner. The sagging tendency and blow moldability of the parisons, which were intermediate products, and the transparency of the bottles obtained were determined or evaluated by the methods described above. The results are shown in Table 10 below.

Examples 8 to 10

Example 5 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of the solid phase polymerization were changed as shown in Table 8 below to carry out esterification, melt polycondensation and solid phase polymerization to prepare copolyesters. The obtained copolyesters were similarly tested for the content of structural units and physical properties. The results are shown in Table 8 below.

The copolyesters obtained in these Examples 8 to 10 were extrusion-blown into bottles in the same manner. The sagging tendency and blow moldability of the parisons, which were intermediate products, and the transparency of the bottles obtained were determined or evaluated by the methods described above. The results are shown in Table 10 below.

Comparative examples 1 to 4

(1) Example 5 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of solid phase polymerization were changed as shown in Table 9 below to carry out esterification, melt polycondensation and solid phase polymerization, thereby preparing copolyesters (Comparative Examples 1 to 3) and a homopolyester (Comparative Example 4). The obtained copolyesters and homopolyester were similarly tested for the content of structural units and physical properties. The results are shown in Table 9 below.

The copolyester obtained in Comparative Example 3, which had a low melting point, was tested on this occasion for the MFR and intrinsic viscosities at a shear rate of 0.1 rad/s (η1) and at a shear rate of 100 rad/s (η2), each at 240°C.

(2) The copolyesters and homopolyesters obtained in these Comparative Examples 1 to 4 were extrusion-blow-molded into bottles in the same manner (However, the copolyester obtained in Comparative Example 3, which had a low melting point, was first melt-extruded at 240°C and then blow-molded). The sagging tendency and blow-moldability of the parisons, which were intermediate products, and the transparency of the bottles obtained were determined or evaluated by the methods described above. The results are shown in Table 10 below.

(3) In the above extrusion blow molding (2), the copolyesters having a large content of triol units obtained in Comparative Examples 1 and 2 gave parisons which had turned white during the sagging due to the formation of spherulites. These parisons caused whitening or breakage of the lower part when molded into bottles, whereby they could not be blown uniformly. Furthermore, the obtained bottles, in which gel-like agglomerates were formed at the transparent part of the body, had a noticeably poor appearance.

In Comparative Example 3 in which cyclohexanedimethanol was copolymerized, the obtained copolyester had a lowered melting point and therefore caused rather severe sagging in extrusion blow molding despite low-temperature molding, accordingly it was poor in moldability.

In Comparative Example 4, bottles could not be produced due to severe sagging during extrusion blow molding.

The designations used in Examples 5 to 10 above and Tables 7 to 9 below are as shown in Table 6 below.

Table 6 Name Connection

TPA Terephthalic acid

EC ethylene glycol

CHDM 1,4-cyclohexanedimethanol

HEPP 2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxy- ethoxy)phenyl]propane (compound of the above formula (XIII))

HEB 1,4-bis(2-hydroxyethoxy)-2-(2-hydroxyethyl)benzene (compound of the following formula (XIV))

DEG Diethylene glycol Table 7

1) Based on the sum of total diol units and total triol units. Table 8

1) Based on the sum of total diol units and total triol units. Table 9

1) Based on the sum of total diol units and total triol units. Table 10

1) Difference between maximum and minimum diameter of the parison.

The following can be seen from Tables 7 to 10.

The copolyesters of Examples 5 to 10 which use HEPP or HEB, each of which is a triol component (V) or a triol component (VI), in amounts within the range specified in the present invention and which accordingly have triol units [triol units (I) and/or triol units (II)] derived from these components, all have excellent melt moldability, particularly extrusion blowability. In the production of bottles by extrusion blow molding, in all examples, the sinking time of the extruded parison is in the range of 15 to 25 seconds, the difference between the maximum and minimum diameter of the parison is not more than 1 cm, the bottle production is at least 120 units per hour, with fewer than 10 bottles per 100 being defective, the bottles obtained have an average wall thickness of 0.25 to 0.55 mm, which thus demonstrates excellent blow moldability, and the bottles have a haze value of not more than 3 and a b value of not more than 1, which thus demonstrates excellent transparency.

On the other hand, although the copolyester of Comparative Example 1 contains units [triol units (I)] of HEPP which is a triol component (V), containing them in too large an amount outside the range specified in the present invention; and although the copolyester of Comparative Example 2 contains units [triol units (II)] of HEB which is a triol component (VI), containing them in too large an amount outside the range specified in the present invention, both have too high a melt viscosity (η1) and therefore have a settling time exceeding 25 seconds, are poor in extrusion blow molding productivity, and give bottles having too large an average wall thickness and large unevenness in thickness and poor transparency.

The copolyester of Comparative Example 3, which contains neither triol units (I) nor triol units (II) but instead contains units of cyclohexanedimethanol (CHDM), has a low melting point of 225°C and, although it was extrusion blow molded at a low temperature (240°C), has a short settling time of 9 seconds, thus proving bad settling, thereby having poor extrusion blowability. Besides, the obtained bottles have greater unevenness in thickness compared with Examples 5 to 10 and are also inferior in transparency.

The homopolyester of Comparative Example 4, which contains neither triol units (I) nor triol units (II) and corresponds to conventional polyethylene terephthalate, is, as stated above, difficult to process in practice by extrusion blow molding.

Example 11

(1) From 100 parts by weight of terephthalic acid, 44.83 parts by weight of ethylene glycol, 9.52 parts by weight of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane of the following formula (XV) (hereinafter referred to as "EOBPA")

and 0.108 parts by weight of 2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxyethoxy)phenyl]propane of the formula (XIII) described above. To the slurry were added 0.020 parts by weight of germanium dioxide, 0.015 parts by weight of phosphoric acid, 0.015 parts by weight of manganese acetate and 0.015 parts by weight of tetraethylammonium hydroxide. The resulting slurry was heated to a temperature of 250°C under pressure (absolute pressure: 2.5 kg/cm²) to carry out esterification up to an esterification ratio of 95%, thereby preparing a compound having a low polymerization degree. The thus obtained compound was melt polycondensed under reduced pressure of 133 Pa (1 mmHg) and at a temperature of 270 °C to give a copolyester prepolymer with an intrinsic viscosity of 0.70 dl/g. The prepolymer was extruded through a die into a strand, which was then cut into cylindrical chips (diameter: 2.5 mm, length: 3.5 mm). The prepolymer had an MFR of 36 g/10 min.

The copolyester prepolymer chips thus obtained, after being predried at a temperature of 150 °C for 5 hours, were solid-phase polymerized under reduced pressure of 13 Pa (0.1 mmHg) at a temperature of (about 205 °C) about 25 °C lower than the melting point for 29 hours to give a high molecular weight copolyester.

(2) The copolymer obtained in the above (1) was examined for the content of each structural unit by the methods described above. The content of terephthalic acid units, ethylene glycol units, EOBPA units, HEPP units or diethylene glycol units was as shown in Table 12.

(3) The copolymer obtained in the above (1) was tested for physical properties according to the methods described above, whereby, as shown in Table 12 below, an intrinsic viscosity of 1.21 dl/g, an MFR at a temperature of (melting point + 40°C) (269°C) of 1.1 g/10 min, and melt viscosities at the same temperature and at a shear rate of 0.1 rad/s (η₃) and at a shear rate of 0.1 rad/s (η₃) respectively. velocity of 100 rad/s (η₄) of 1.32 · 10⁵ poise and 2.52 · 10⁴ poise, respectively, resulting in a value for (1/3)log₁₀(η₄/η₃) of -0.24.

The copolyester was further tested for Tg and Tm by the procedure described above, which were found to be 78°C and 229°C, respectively, as shown in Table 12 below.

(4) The copolyester was extrusion blow-molded into bottles (designed capacity: 1000 ml, design wall thickness: 0.4 mm) using an extrusion blow molding machine (hollow molding machine TB-ST-6P, manufactured by Suzuki Iron Works). According to the procedures described above, the obtained parison was tested for sagging tendency and blow moldability, and the bottles were tested for transparency and impact resistance, to obtain the results shown in Table 15 below.

Examples 12 to 14

Example 11 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of solid phase polymerization were changed as shown in Table 12 below to carry out esterification, melt polycondensation and solid phase polymerization, thereby preparing copolyesters. The obtained copolyesters were similarly tested for the content of structural units and physical properties. The results are shown in Table 12 below.

The copolyesters obtained in these Examples 12 to 14 were extrusion-blown into bottles in the same manner. The sagging tendency and blow moldability of the parisons, which were intermediate products, as well as the transparency and impact resistance of the bottles obtained were determined or evaluated by the methods described above. The results are shown in Table 15 below.

Examples 15 to 17

Example 11 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of solid phase polymerization were changed as shown in Table 13 below to carry out esterification, melt polycondensation and solid phase polymerization, thereby preparing copolyesters. The obtained copolyesters were similarly tested for the content of structural units and physical properties. The results are shown in Table 13 below.

The copolyesters obtained in these Examples 15 to 17 were extrusion-blown into bottles in the same manner. The sagging tendency and blow moldability of the parisons, which were intermediate products, as well as the transparency and impact resistance of the bottles obtained were determined or evaluated by the methods described above. The results are shown in Table 15 below.

Comparative examples 5 to 9

(1) Example 11 was repeated except that the kind and amount of the diol component and triol component and the temperature and time of solid phase polymerization were changed as shown in Table 14 below to carry out esterification, melt polycondensation and solid phase polymerization, thereby preparing copolyesters (Comparative Examples 5 to 8) and a homopolyester (Comparative Example 9). The obtained copolyesters and homopolyester were similarly tested for the content of structural units and physical properties. The results are shown in Table 14 below.

The copolyester obtained in Comparative Example 7, which was amorphous, was tested on this occasion for the MFR and intrinsic viscosities at a shear rate of 0.1 rad/s (η₃) and at a shear rate of 100 rad/s (η₄), each at 240°C.

(2) The copolyesters and homopolyesters obtained in these Comparative Examples 5 to 9 were extrusion-blow-molded into bottles in the same manner. The sagging tendency and blow moldability of the parisons, which were intermediate products, and the transparency and impact resistance of the obtained bottles were determined or evaluated by the methods described above. The results are shown in Table 15 below.

(3) In the above extrusion blow molding (2), in Comparative Example 6, the parison became white during the descent due to the formation of spherulites. The parison caused whitening or breakage of the lower part when molded into bottles, whereby it could not be blown uniformly. Furthermore, the obtained bottles, in which gel-like agglomerates were formed at the transparent part of the body, had a noticeably poor appearance.

In Comparative Example 7, the copolyester obtained by melt polycondensation, which was amorphous, could not be polymerized in solid phase. Therefore, Table 14 below gives the physical properties of the copolyester prepolymer obtained by melt polycondensation and also the results of evaluation on the sagging tendency and the blow moldability of the parison in blow molding, wherein the copolyester prepolymer was temperature of 240ºC, as well as the transparency and impact resistance of the bottles obtained.

In Comparative Example 9, bottles could not be produced due to severe sagging during extrusion blow molding.

The designations used in the above Examples 11 to 17 and the following Tables 12 to 14 are as shown in Table 11 below.

Table 11 Name Connection

TPA Terephthalic acid

EC ethylene glycol

EOBPA 2,2-bis [4-(2-hydroxyethoxy)phenyl]propane (compound of the above formula (XV))

BHEB 1,4-bis(2-hydroxyethoxy)benzene (compound of the following formula (XVI))

CHDM 1,4-cyclohexanedimethanol

HEPP 2-[4-(2-hydroxyethoxy)phenyl]-2-[3'-(2-hydroxyethyl)-4'-(2-hydroxy- ethoxy)phenyl]propane (compound of the above formula (XIII))

HEB 1,4-bis(2-hydroxyethoxy)-2-(2-hydroxyethyl)benzene (compound of the following formula (XIV))

DEG Diethylene glycol Table 12

1) Based on the sum of total diol units and total triol units. Table 13

1) Based on the sum of total diol units and total triol units. Table 14

1) Based on the sum of total diol units and total triol units. Table 15

1) Difference between maximum and minimum diameter of the parison.

The following can be seen from Tables 12 to 15 above.

The copolyesters of Examples 11 to 17 which use EOBPA or BHEB, each of which is a diol component (VII) or a diol component (VIII), and HEPP or HEB, each of which is a triol component (V) or a triol component (VI), in amounts within the range specified in the present invention and which accordingly have diol units derived from these diol components [diol units (III) or diol units (IV)] and triol units derived from these triol components [triol units (I) and/or triol units (II)], all have excellent melt moldability, particularly extrusion blowability. In the manufacture of bottles by extrusion blow molding, in all examples, the sinking time of the extruded parison is in the range of 10 to 25 seconds, the difference between the maximum and minimum diameter of the parison is not more than 1 cm, the bottle production is at least 120 pieces per hour, with fewer than 10 parisons per 100 bottles being defective, the bottles obtained have an average wall thickness of 0.25 to 0.55 mm, thus proving excellent blow moldability, the bottles have a haze value of not more than 4 and a b value of not more than 4, thus proving excellent transparency, and the above results from 5 drop tests are good.

On the other hand, although the copolyester of Comparative Example 5 contains structural units [diol units (III)] of EOBPA which is a diol component (VII), but does not contain triol units (I) or triol units (II); although the copolyester of Comparative Example 6 contains structural units [diol units (III)] of EOBPA which is a diol component (VII) and structural units [triol units (I)] of HEPP which is a triol component (V), but contains the latter in too large an amount outside the range specified in the present invention; although the copolyester of Comparative Example 7 contains structural units [diol units (III)] of EOBPA which is a diol component (VII) and structural units [triol units (I)] of HEPP which is a triol component (V), it contains the former in too large an amount outside the range specified in the present invention; and the copolyester of Comparative Example 8 which contains alicyclic diol units (i.e., diol units of CHDM) other than the diol units (III) or diol units (IV); all are not applicable to melt molding, particularly extrusion blow molding. All of these copolyesters give extruded parisons poor in both sagging tendency and blow moldability, and all give bottles inferior in transparency and impact resistance.

The homopolyester of Comparative Example 9, which does not contain diol units (III), diol units (IV), triol units (I) or triol units (II), is, as stated above, difficult to process in practice by extrusion blow molding.

Example 18 (Preparation of a modified polyester using HEPP obtained in Example 1 as a crosslinking component)

A slurry was prepared from 100.00 parts by weight of terephthalic acid, 44.84 parts by weight of ethylene glycol, 0.54 parts by weight (0.25 mol in terms of terephthalic acid) of HEPP. To the slurry were added 1.8 parts by weight (150 ppm in terms of the theoretical amount of polyester produced) of germanium dioxide and 0.95 parts by weight (100 ppm in terms of the theoretical amount of polyester produced) of phosphoric acid. The resulting slurry was heated to a temperature of 250°C under reduced pressure (absolute pressure: 2.5 kg/cm²) to conduct esterification up to an esterification ratio of 95%, thereby preparing a compound having a low degree of polymerization. The thus obtained compound was melt polycondensed under a reduced pressure of 40 Pa (0.3 mmHg) and at a temperature of 270 °C to give a copolyester prepolymer with an intrinsic viscosity of 0.70 dl/g. The prepolymer was extruded through a die into a strand, which was then cut into cylindrical chips (diameter: 2.5 mm, length: 3.5 mm).

The prepolymer chips thus obtained, after being predried at a temperature of 150 °C for 5 hours, were subjected to solid-phase polymerization under a reduced pressure of 13 Pa (0.1 mmHg) at a temperature of 225 °C for 6 hours to give a high-molecular modified polyester.

The modified polyester obtained had an intrinsic viscosity of 1.15 dl/g, a melt index at a temperature of 270 °C of 1.2 g/10 min and a melt viscosity at the same temperature and a shear rate of 0.1 rad/s of 210,000 poise.

The modified polyester was hot-pressed at 270ºC into a transparent film with a thickness of 100 microns. The transparent film was observed for appearance and the result is shown in Table 16.

The modified polyester was also evaluated for extrusion blowability. The modified polyester was extruded into a parison through an annular orifice using an extrusion blow molding machine (TB-ST-6P, manufactured by Suzuki Iron Works). The parison was pinched off with a blow mold while it was in the softened state, thereby the opening part was cut and the lower part was connected, and then blow molded into hollow containers with a capacity of 1000 ml and an average wall thickness of 0.4 mm. The moldability and conditions for the hollow containers were evaluated according to the following criteria. The results are shown in Table 16.

Extruded parison produces a cylinder with uniform diameter, and the resulting hollow containers are excellent in smoothness and transparency.

Δ Although the extruded parison yields a cylinder with a uniform diameter, the resulting hollow containers have a poor appearance since they show gel-like agglomerates.

X Extruded parison does not give a cylinder of uniform diameter and has some difficulty in giving hollow containers due to the frequent occurrence of closure in the hollow part of the parison in the softened state. The hollow containers obtained, which carry gel-like agglomerates, have a poor appearance. Table 16

Comparison example 11

Example 18 was repeated except that the type and amount of the crosslinking component used were changed as shown in Table 16, thereby obtaining modified polyesters and transparent films produced therefrom. Evaluation of extrusion blowability was carried out in the same manner as in Example 18. The results are shown in Table 16.

In Comparative Examples 10 and 11, it took longer than in Example 18 for the polyesters to reach the desired degree of polymerization. The transparent films were noticeably poor in appearance, that is, in surface smoothness, cleanliness and lack of gloss, due to the presence of gel-like agglomerate matter. Also, in the molding test of the hollow containers by extrusion blow molding, the containers had noticeably poor appearance due to the formation of gel-like agglomerates.

As is clear from Table 16, the polyethylene terephthalate modified with an aromatic triol of the present invention has a higher polymerization rate and more effectively suppressed the formation of gels and agglomerates compared with the polyethylene terephthalate modified with a conventional crosslinking agent. It is also clear that the polyethylene terephthalate modified with an aromatic triol of the present invention has better extrudability and gives molded articles with better appearance compared with the polyethylene terephthalate modified with a conventional crosslinking agent.

Claims (12)

1. Copolyester comprising: (i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, wherein the copolyester further comprises: (ii) at least one group of triol units selected from: (a) Triol units (I) of the following formula (I) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8; and (b) Triol units (II) of the following formula (II) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and s, t and u are each independently an integer from 1 to 8, in an amount of 0.01 to 1 mol% based on the sum of the number of moles of the total diol units and the number of moles of the triol units of this item (ii). 2. Copolyesters comprising: (i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, wherein the copolyester further comprises: (ii) at least one group of diol units selected from: (a) Diol units (III) of the following formula (III) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and j and k are each independently an integer from 1 to 8; and (b) Diol units (IV) of the following formula (IV) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and m and n are each independently an integer from 1 to 8, and (iii) at least one group of triol units selected from: (a) triol units (I) of formula (I) as defined in claim 1; and (b) triol units (II) of the formula (II) as defined in claim 1, and (iv) wherein the at least one group of diol units selected from diol units (III) and diol units (IV) is contained in an amount of 1 to 15 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the triol units of the above item (iii), and (v) wherein the at least one group of triol units is selected from triol units (I) and triol units (II), in an amount of 0.01 to 1 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol units of the above point (iii). 3. Copolyester according to claim 1 or 2 having an intrinsic viscosity of 0.6 to 1.5 dl/g, measured at 30 ºC in phenol/tetrachloroethane (1/1 by weight) with an Ubbelohde viscometer. 4. A copolyester according to claim 1 or 3 having a melt viscosity (η1) at a temperature of 270°C and at a shear rate of 0.1 rad/s of 5 x 104 to 5 x 106 poise and a melt viscosity (η2) at a temperature of 270°C and at a shear rate of 100 rad/s of 5 x 103 to 5 x 105 poise, wherein the melt viscosities (η1) and (η2) satisfy the following condition 1 - 0.75 ? (1/3)log10(eta2/eta1) ? -0.2 1 , whereby the melt viscosities are measured dynamically with a mechanical spectrometer. 5. Copolyester according to claim 2 or 3 having a melt viscosity (η₃) at a temperature of (melting point + 40°C) and at a shear rate of 0.1 rad/s of 5 x 10⁴ to 5 x 10⁶ poise and a melt viscosity (η₄) at a temperature of (melting point + 40°C) and at a shear rate of 100 rad/s of 5 x 10³ to 5 · 10⁵ poise, wherein the melt viscosities (η₃) and (η₄) satisfy the following condition 2 - 0.7 ? (1/3)log10 (η4 /η3 ) ? -0.2 2 , whereby the melt viscosities are measured dynamically with a mechanical spectrometer. 6. A molded part comprising the copolyester according to any one of claims 1 to 5. 7. A molded article according to claim 6, namely an extrusion blow molded article. 8. A process for producing molded parts comprising extrusion blow molding of the copolyester according to any one of claims 1 to 5. 9. Process for producing the copolyester according to one of claims 1 and 3 to 5. comprising Esterification or transesterification of starting materials, comprising: (1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof; (2) a diol component consisting essentially of ethylene glycol; and (3) a triol component comprising at least one triol selected from: (a) a triol of the following formula (V): in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8; and (b) a triol of the following formula (VI) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and s, t and u are each independently an integer from 1 to 8; in an amount of 0.01 to 1 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol component of this item (3); melt polycondensing the resulting reaction product to produce a polyester prepolymer; and Polymerizing the polyester prepolymer in solid phase. 10. A process for producing the copolyester according to any one of claims 2 to 5, comprising esterification or transesterification of starting materials, comprising: (1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof; (2) a diol component consisting essentially of ethylene glycol and at least one diol selected from (a) a diol of the following formula (VII) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and j and k are each independently an integer from 1 to 8; and (b) a diol of the following formula (VIII) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and m and n are each independently an integer from 1 to 8; in an amount of 1 to 15 mol% based on the sum of the mole numbers of the total diol units and the mole numbers of the triol component of the item (3) described below; and (3) a triol component comprising at least one triol selected from (a) a triol of formula (V) as defined in claim 9; and (b) a triol of formula (VI) as defined in claim 9, in an amount of 0.01 to 1 mol%, based on the sum of the number of moles of the total diol units and the number of moles of the triol component of this item (3); melt polycondensing the resulting reaction product to produce a polyester prepolymer; and Polymerizing the polyester prepolymer in solid phase. 11. Aromatic triol of the following general formula (V) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂-, B is a divalent hydrocarbon radical, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-) and p, q and r are each independently an integer from 1 to 8. 12. Aromatic triol of the following general formula (VI) in which A is a radical of the formula -CH₂CH₂- or of the formula -CH(CH₃)CH₂- and s, t and u are each independently an integer from 1 to 8.